Practically since hip-hop was invented, its lyrical content has been the subject of much debate. But while mainstream hip-hop offers much about which to raise eyebrows, underground rap is really where the craziness begins.

Not that that's all bad. Where mainstream rap is constrained by certain radio-ready formulas, underground rap needs to worry about no such rules. In underground rap, artists can be as creative, clever, or just as crazy as they want.

In certain underground rap circles, shocking, outrageous content is prized -- no subject is too taboo. Here are five underground rap artists whose lyrics often aren't for the faint of heart.

Cage: The underground rap artist born Chris Palko was known at the beginning of his career for broaching uncomfortable subjects and often being "Crazy for the sake of being crazy," as he himself put it in interviews. Much of his early material told long, involved tales of drug use and included violent fantasies.

Cage has much matured as an underground rap artist, these days, and often draws from his own uncomfortable personal history for lyrics. He never shies away from taboo subjects when discussing them, though, and Cage songs still broach subjects like child abuse, mental illness, and addiction.

Necro: Necro often collaborated with Cage when the two rappers were younger. However, as Cafe's style of underground rap became more confessional, Necro's became more and more fantasy-driven. These days, Necro is considered largely to be a horrorcore artist whose music bears a metal influence and whose lyrical subjects touch on violence and the occult.

Twiztid: This underground rap group is signed to Insane Clown Posse's Psychopathic Records, and Twiztid lyrics live up to the precedent set by the label. Twiztid lyrics definitely fall under the category of horrorcore, and unabashedly so. With album titles like Heartbroken and Homicidal, it's clear that Twiztid lyrics are often uber-violent.

From the group's first album, Mostateless, Twiztid lyrics have included raps about murder, drug use, and even more out-there Twiztid lyrics subjects like the undead. That's not to say that Twiztid lyrics are meant to be taken literally, though.

The kind of horror and mayhem expressed in Twiztid lyrics are clearly flights of fantasy influenced by horror movies, comic books, and the like. The group has cited rock acts like KISS as an influence on Twiztid lyrics, for example.

Insane Clown Posse: Insane Clown Posse lyrics influenced Twiztid lyrics, and those of other similar acts. In fact, Insane Clown Posse lyrics were actually influenced by those of earlier Detroit acts like Esham and his group Natas. Those artists' "acid rap" style influenced certain aspects of Insane Clown Posse lyrics, like a particular psychedelic vibe and out-there imagery.

But Insane Clown Posse lyrics were also influenced by their beloved comic books and horror movies. That filtered into Insane Clown Posse lyrics that never shied away from outrageous tales of violence and gore.

Still, like Twiztid, Insane Clown Posse lyrics were never meant to be taken seriously. In fact, a close reading of Insane Clown Posse lyrics shows that the violence only befalls evil people who perhaps deserve an unhappy end.

The Insane Clown Posse lyrics from the band's Dark Carnival mythical cycle also served a didactic purpose. It turned out all of those crazy Insane Clown Posse lyrics were actually meant to serve as moral fables, instructing listeners on how not to act. Still, the pictures they painted were definitely shocking at the surface.

Resource Box

If anyone best represents the certain crazy, colorful, unique underground rap scene known as horrorcore in its current form, it's Insane Clown Posse. They've been going for more than two decades now, so to learn more about the group's influential history in underground rap, visit the official Insane Clown Posse web site at http://www.insaneclownposse.com